Decoding apparatus, dequantizing method, distribution determining method, and program thereof

1. A decoding apparatus comprising: a random-number generating section that generates random numbers according to distribution of original data corresponding to respective quantization indexes of entropy-encoded code data; a dequantization section that sets respective quantization indexes of the entropy-encoded data to a quantization index of interest in order, wherein if a dequantization value can be estimated for the quantization index of interest based on a threshold comparison with neighboring quantization indexes, the dequantization section generates a dequantization value for the quantization index of interest using a dequantization-value estimating section without using the random numbers, and if the dequantization value cannot be estimated for the quantization index of interest, the dequantization section generates the dequantization value for the quantization index of interest using the random numbers generated by the random-number generating section, and the dequantization section includes a dequantization-value outputting section that generates and outputs the dequantization value to be used as decoded data based on the dequantization value generated by the dequantization section.

2. The decoding apparatus according to claim 1 , further comprising: a distribution estimating section that generates distribution information representing frequency distribution of quantization indexes included in the code data, wherein: the random-number generating section uses the distribution information generated by the distribution estimating section as distribution information of the original data.

3. The decoding apparatus according to claim 1 , wherein the random-number generating section generates the random numbers within a preset range.

4. The decoding apparatus according to claim 1 , wherein the dequantization-value outputting section uses the random numbers generated by the random-number generating section only when the value of a given quantization index to be processed is 0.

5. The decoding apparatus according to claim 1 , wherein the dequantization section generates the dequantization value corresponding to a given quantization index using the value of the given quantization index to be processed and a value of another quantization index having a predetermined relation with the given quantization index.

6. The decoding apparatus according to claim 5 , wherein: the dequantization-value outputting section uses the random numbers generated by the random-number generating section when all differences between the value of the given quantization index and the value of the other quantization index is 0; and the dequantization-value outputting section uses the dequantization values generated by the dequantization-value estimating section when at least one difference is not equal to 0.

7. The decoding apparatus according to claim 2 , wherein: the distribution estimating section generates at least one of a variance of the quantization indexes and a standard deviation of the quantization indexes as the distribution information; and the random-number generating section generates the random numbers according to a Laplace distribution corresponding to the at least one of the variance and the standard deviation generated by the distribution estimating section.

8. The decoding apparatus according to claim 7 , wherein the distribution estimating section calculates at least one of a variance of the Laplace distribution and a standard deviation of the Laplace distribution so as to minimize a sum of area differences between histograms of the quantization index values and the Laplace distribution, with regard to respective quantization intervals corresponding to respective quantization index values.

9. The decoding apparatus according to claim 3 , wherein the random-number generating section generates the random numbers within the range according to a width of a quantization interval corresponding to each quantization index.

10. The decoding apparatus according to claim 1 , further comprising: a standard-deviation estimating section that acquires a standard deviation of transform coefficients corresponding to the quantization indexes; a multiplying section that multiplies the standard deviation acquired by the standard-deviation estimating section by a preset value; and an upper-limit-value acquiring section that acquires an upper limit value of generated random numbers, wherein the random-number generating section uniformly generates the random numbers, with smaller one of the standard deviation multiplied by the preset value by the multiplying section and the upper limit value acquired by the upper-limit-value acquiring section being an upper limit.

11. The decoding apparatus according to claim 1 , further comprising: a frequency distribution measuring section that measures appearance frequency of the quantization indexes; a histogram normalizing section that generates normalized histograms based on the appearance frequency measured by the frequency distribution measuring section; an N value range acquiring section that determines an addition range in which frequency distribution of the quantization indexes is added; and a distribution estimating section that determines at least one of a standard deviation and a variance based on the histograms generated by the histogram normalizing section and the addition range determined by the N value range acquiring section.

12. A computer-implemented dequantizing method comprising: using a controller to generate random numbers according to distribution of original data corresponding to respective quantization indexes of entropy-encoded code data; using a controller to generate respective quantization indexes of the entropy-encoded code data to a quantization index of interest in order, wherein if a dequantization value can be estimated for the quantization index of interest based on a threshold comparison with neighboring quantization indexes, generating the dequantization value for the quantization index of interest by a dequantization-value estimating section of the controller without using random numbers generated by a random-number generating section of the controller, and if the dequantization value cannot be estimated for the quantization index of interest, generating the dequantization value for the quantization index of interest using the random numbers; and using a controller to output decoded data based on the dequantization value generated.

13. The dequantizing method according to claim 12 , further comprising: generating distribution information representing frequency distribution of quantization indexes included in the code data, wherein: the random-number generating uses the generated distribution information as distribution information of the original data.

14. The dequantizing method according to claim 12 , wherein the random-number generating generates the random numbers within a preset range.

15. The dequantizing method according to claim 14 , wherein the random-numbers are generated within the range according to a width of a quantization interval corresponding to each quantization index.

16. The dequantizing method according to claim 12 , wherein the decoding uses the generated random numbers only when the value of a given quantization index to be processed is 0.

17. The dequantizing method according to claim 12 , wherein the dequantization value is generated corresponding to a given quantization index using the value of the given quantization index to be processed and a value of another quantization index having a predetermined relation with the given quantization index.

18. The dequantizing method according to claim 17 , wherein: the dequantization values using the generated random numbers are used when all differences between the value of the given quantization index and the value of the other quantization index is 0; and the dequantization values not using the generated random numbers are used when at least one difference is not equal to 0.